ApexSampleCode.xml

<apex:page controller="DreamhouseProspects">
        <apex:pageBlock >
            <apex:sectionHeader title="Leads" subtitle="Home"/>
            <apex:form >
                <div style="text-align:center;">
                    <apex:commandButton action="{!URLFOR($Action.Lead.New)}" value="New"/>
                </div>
                <apex:outputLabel value="Sort: " for="sortList" />
                <apex:selectList value="{! sortOrder}" size="1" id="sortList">
                    <apex:selectOption itemvalue="LastName" />
                    <apex:selectOption itemvalue="FirstName" />
                </apex:selectList>
                <apex:commandButton value="Sort Table" action="{!sortList}" reRender="leads_list"/>
                <apex:pageBlockTable value="{! leads }" var="ct" id="leads_list">
                    <apex:column headerValue="First Name">
                        <apex:outputLink value="/{! ct.Id}">{! ct.FirstName }</apex:outputLink>
                    </apex:column>
                    <apex:column value="{! ct.LastName }"/>
                    <apex:column value="{! ct.Email }"/>
                    <apex:column value="{! ct.Phone }"/>
                </apex:pageBlockTable>              
            </apex:form>
        </apex:pageBlock>
</apex:page>

ApexSampleCodeLightning.xml

<apex:page controller="DreamhouseProspects" lightningStylesheets="true">
    <apex:slds rendered="{! !isClassic}"/>
    <apex:pageBlock >
        <apex:form >
            <apex:outputPanel rendered="{! isClassic}">
                <apex:sectionHeader title="Leads" subtitle="Home"/>
                <div style="text-align:center;">
                    <apex:commandButton action="{!URLFOR($Action.Lead.New)}" value="New"/>
                </div>
                <apex:outputLabel value="Sort: " for="sortList" />
                <apex:selectList value="{! sortOrder}" size="1" id="sortList">
                    <apex:selectOption itemvalue="LastName" />
                    <apex:selectOption itemvalue="FirstName" />
                </apex:selectList>
                <apex:commandButton value="Sort Table" action="{!sortList}" reRender="leads_list"/>
            </apex:outputPanel>
            <apex:outputPanel rendered="{! !isClassic}">
                <div class="slds-page-header">
                    <div class="slds-grid">
                        <div class="slds-col slds-has-flexi-truncate" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
                            <div class="slds-media slds-no-space slds-grow">
                                <div class="slds-media__figure">
                                    <svg class="slds-icon slds-icon-standard-user .slds-icon_small" aria-hidden="true">
                                        <use xlink:href="{!URLFOR($Asset.SLDS, 'assets/icons/standard-sprite/svg/symbols.svg#lead')}"></use>
                                    </svg>
                                </div>
                                <div class="slds-media__body">
                                    <p class="slds-text-title_caps slds-line-height_reset">Lead</p>
                                    <h1 class="slds-page-header__title slds-m-right_small slds-align-middle slds-truncate"
                                        title="this should match the Record Title">Home</h1>
                                </div>
                            </div>
                            <div class="slds-grid slds-grid_vertical-align-end slds-m-vertical_small">
                                <div class="slds-size_1-of-6 ">
                                    <apex:outputLabel value="Sort: " for="sortListLightning" styleClass="slds-form-element__label" />
                                    <div class="slds-select_container">
                                        <apex:selectList value="{! sortOrder}" size="1" id="sortListLightning" styleClass="slds-select">
                                            <apex:selectOption itemvalue="LastName" />
                                            <apex:selectOption itemvalue="FirstName" />
                                        </apex:selectList>
                                    </div>
                                </div>
                                <div class="slds-no-flex slds-m-left_x-small">
                                    <apex:commandButton value="Sort" action="{!sortList}" reRender="leads_list" styleClass="slds-button slds-button_neutral"/>
                                </div>
                            </div>
                        </div>
                        <div class="slds-col slds-no-flex slds-grid slds-align-top">
                            <apex:commandButton action="{!URLFOR($Action.Lead.New)}" value="New" styleClass="slds-button slds-button_neutral"/>
                        </div>
                    </div>
                </div>
            </apex:outputPanel>
            <apex:pageBlockTable value="{! leads }" var="ct" id="leads_list">
                <apex:column headerValue="First Name">
                    <apex:outputLink value="/{! ct.Id}">{! ct.FirstName }</apex:outputLink>
                </apex:column>
                <apex:column value="{! ct.LastName }"/>
                <apex:column value="{! ct.Email }"/>
                <apex:column value="{! ct.Phone }"/>
            </apex:pageBlockTable>              
        </apex:form>
    </apex:pageBlock>
</apex:page>