html

<div class="search-block">
	<div class="block-logo item-block">
		<img src="https://gc.onliner.by/images/logo/onliner_logo.v3.png?token=1500276935">
	</div>
	<div class="block-search item-block">
		<input type="text" name="search" placeholder="Введите текст для опоиска всякой хуйни" />
	</div>
	<div class="block-social item-block">
		<button>Войти</button>
	</div>
</div>

цсс

.search-block {
		width: 100%;
	}
	.search-block .item-block {
		float: left;
		text-align: center;
		width: calc(100%/3);
	}
	.search-block .item-block input {
		width: 100%;
		height: 40px;
	}
	.search-block .item-block button {
		border: 1px solid #ccc;
		height: 40px;
		width: 150px;
		background: #fff;
		outline: none;
		border-radius: 3px 0 0 3px;
	}
	.search-block .item-block button:hover {
		background: #999;
	}