Less font example

fonts.less

#font {
    @helvetica-stack:        "Helvetica Neue", Arial, sans-serif;
    @helvetica-heavy-stack:  @helvetica-stack;
    @helvetica-light-stack:  "HelveticaNeueW01-Thin", @helvetica-stack;
    @helvetica-italic-stack: "HelveticaNeue-Italic", @helvetica-stack;

    // sizes
    @base-font-size: 14px;
    .big() {
        font-size: 4 * @base-font-size;
    }
    .medium() {
        font-size: 3 * @base-font-size;
    }
    .normal() {
        font-size: @base-font-size;
    }
    .small() {
        font-size: .75 * @base-font-size;
    }

    // weights
    .heavy() {
        font-weight: bold;
        font-family: @helvetica-heavy-stack;
    }
    .medium() {
        font-weight: medium;
        font-family: @helvetica-stack;
    }
    .light() {
        font-weight: 200;
        font-family: @helvetica-light-stack;
    }

    // styles
    .italic() {
        font-style: italic;
        font-family: @helvetica-italic-stack;
    }
}

main.less

h1 {
    #font .big;
    #font .heavy;

    // except when it's inside an article...
    article & {
        #font .medium;
    }
}

h2 {
    #font .medium;
    #font .light;
}