html - Vertical space between two inline-block and a block element

Question

.rectangle {
    width: 420px;
    height: 143px;
    color: #fff;
    background: rgba(0, 0, 0, 0.7);
    padding: 20px 0px 20px 10px;
    position: relative;
    display: inline-block;
    vertical-align: top;
}

.triangle {
    width: 0;
    height: 0;
    border-top: 92px solid transparent;
    border-bottom: 92px solid transparent;
    border-left:45px solid rgba(0, 0, 0, 0.7);
    display: inline-block;
}

.block {
  width: 200px;
  height: 80px;
  background: red;
}

<div class="rectangle"></div><!--
--><div class="triangle"></div>
<div class="block"></div>

Answer 1

The other answers provide solutions, but not the why this happens:

Some given funny joke
-----^---------^-^

In that string I've marked three characters. Those three have so called 'decenders' (e.g.: the loop under the G, the legs under the Y and J).
When you declare something inline-block, it gets the properties of both block and inline elements. The inline elements are often text (e.g. a or span), thus have decenders, thus your div has room for decenders.

This is why setting line-height:0; font-size:0; does the trick.